The overhead and manpower needed to maintain gnome2 by themselves in addition to developing Unity?
Maybe if the GNOME project had maintained the 2.x series alongside 3 it would still had been an option in Ubuntu.

Exactly, they did not give users a choice. I don't understand why anyone would consider this a good thing.

This is really nothing new. The same thing happened when distros changed their default DE from KDE1 to KDE2, KDE2 to KDE3, GNOME to GNOME2 or whatever. You got a new default and if you wanted to stay with the old stuff there was some work to do on your own.

I think this is bad for an open source operating system.

Much OSS software is totalitarian and has always been. Linus (dictator for life, remember?) decides what goes in the official kernel, Theo decides what goes in OpenBSD, Canonical decides the direction of Ubuntu, RedHat decides the direction of RHEL etc etc.

"The overhead and manpower needed to maintain gnome2 by themselves in addition to developing Unity?
Maybe if the GNOME project had maintained the 2.x series alongside 3 it would still had been an option in Ubuntu."

Gone Fishing just installed it and says it works, so it shouldn't have been that difficult for Canonical to work it out back then.